The present application broadly relates to a new and improved construction of a sealing shroud centrifugal or rotary pump, hereinafter simply referred to as a centrifugal pump.
Generally speaking, the sealing shroud centrifugal pump of the present invention comprises a pump housing and a sealing shroud which, on one side, is provided with a motor driven permanent-magnet rotor, whereas on the other side of the sealing shroud a second permanent-magnet rotor is mechanically connected with a pump impeller rotatably mounted on a stationary axle or shaft. This pump impeller, on its rear side, faces a sealing shroud bottom or base, whereas its front side faces a suction connection of the pump housing also containing a delivery or pressure connection.
Centrifugal pumps of the aforementioned type are known from German Patent Publication No. 2,620,502, published Nov. 25, 1976, in which the axle or shaft is at least partially supported at the sealing shroud bottom or base. This can result in an unwanted mechanical loading of the sealing shroud and can also cause difficulties with the equalizing of pressure differences between the front and rear of the pump impeller.
With pump impellers rotating with the shaft in a sealing shroud pump (without shroud base or bottom) it is common practice to partly equalize the pressure differences, insofar as they are not required for feeding a subsidiary or auxiliary flow for cooling and for lubrication of the rear bearing. For this purpose equalizing holes or openings were made in the pump impeller which reach from the rear of the pump impeller to the inside of the pump impeller. That these measures are associated with power losses and require that the axial bearings take up the remaining axial forces is shown by all the publications; compare, for instance, German Patent Publication No. 2,733,631, Swiss Pat. No. 529,929 and European Published Pat. No. 0,078,345.
German Published Pat. No. 2,733,631 provides for the equalizing of the fluctuating axial forces through a control of the throughput of the equalizing hole or opening of the pump impeller, which, at the least, can lead to unwanted disturbances of the pump impeller throughflow and subsequent loss of power.
In the aforementioned European Published Pat. No. 0,078,345 there is even provided a control apparatus in the pump housing to increase the area or cross-section of the equalizing openings which is controlled by the axial position of the shaft.
In the aforementioned Swiss Pat. No. 529,929 wearable axial main bearings and axial auxiliary bearings are provided, whose wear allow, under certain operating conditions, an axial positional movement of the pump impeller and which is supposed to result in a reduction of the axial forces. So far as this is even possible, in the case of changing operating conditions, and this is not seldom the case, there is always required a new wear and a new so-to-speak "working in" of the wearable axial bearings, which finally leads to total wear of the axial bearing.
Equalizing openings in the inside of the pump impeller have not been shown to be sufficiently advantageous and the control of the throughflow depending on axial position has also brought no useful improvement.